The present disclosure relates generally to the field of vehicle braking systems. To be more precise, a hydraulic vehicle braking system equipped with an electromechanical actuator is described.
Electromechanical actuators have already been used for some time in vehicle braking systems or have been proposed for such a use. In the case of hydraulic braking systems, electromechanical actuators are employed, for example, for realising an electrical parking brake function (EPB). In the case of electromechanical braking systems (EMB), they replace the conventional hydraulic cylinders at the wheel brakes.
Owing to technical advances, the efficiency of the electromechanical actuators has continually increased. It was therefore considered to use such actuators also for implementing modern brake control functions. Such brake control functions include an antilock braking system (ABS), a traction control system (TCS) or an electronic stability program (ESP), also referred to as vehicle stability control (VSC). WO 2006/111393 A1 and corresponding U.S. Pat. No. 8,540,324 B2, the disclosures of which are incorporated by reference herein in entirety, for instance, teaches a hydraulic braking system having a highly dynamic electromechanical actuator which performs the pressure modulation in the brake control mode. The actuator is provided to actuate a master cylinder of the braking system.
Owing to the high dynamics of the electromechanical actuator, the hydraulic components of the braking system known from WO 2006/111393 A1 can be reduced to a single 2/2-way valve per wheel brake. To realise wheel-individual pressure modulations, the valves are then driven individually or in groups in multiplex operation.
However, the minimising to only one valve per wheel brake also results in problems, such as an undesired pressure equalisation when valves are opened simultaneously, which have to be solved again in a complex manner (cf. WO 2010/091883 A1 and corresponding U.S. Patent Publication No. 2012/0013173 A1, the disclosures of which are incorporated by reference herein in entirety). A further disadvantage is that multiplex operation requires an electromechanical actuator whose dynamic range has to be greater by at least a factor of the order or 4 compared with conventional electromechanical actuators.